A high-voltage insulator of the aforementioned type is described in DE 694 762 C. This high-voltage insulator has a metal cap and a bar insulator joined to the metal cap. Formed in the metal cap is a groove, into which an annular clamping head of the bar insulator penetrates, thereby forming the joint. A hollow space present between the cap and the clamping head is filled with a layer of a hardening binder. To introduce the binder and to ensure uniform curing of the same, the cap is provided with channels. To prevent penetration of water, these channels are closed with an elastic compound after the binder has been introduced and cured.
The production of such a high-voltage insulator is relatively complex, since the binder has to be introduced from the outside through the metal cap into the hollow space delimited by two joining parts. Moreover, when the binder is introduced through the channels, air bubbles or water can get into the hollow space and thereby reduce the dielectric strength of the insulator.
DE 533 573 C describes a high-voltage insulator used as a support for a high-voltage line, with a hollow insulating body, which is closed at one end, is cemented into a grounded mount and carries a cap supporting the high-voltage line.
CH 89 623 A describes a high-voltage insulator in which the outer surface of an insulating body has within a hollow metal cap, a bead-like thickening, beyond which the cap protrudes. A high electric field strength, and consequently partial discharge or creepage sparking, at the triple point of the metal cap, insulating body and air are thus avoided.
A further high-voltage insulator is described in WO 2006/053452 A1. The high-voltage insulator described is part of a hollow cooling element formed as a heat pipe and serving for the removal of heat from a generator discharge line. It has in a coaxial arrangement a mechanically supporting insulating tube composed of a polymer reinforced with fibers and/or filler and of coaxially held diffusion barriers as well as two hollow metal armatures, which are adhesively bonded in a vacuum-tight manner to the two ends of the insulating tube that are respectively formed as a supporting ring. An adhesive-bonding joint is provided between an adhesive-bonding surface of each of the two supporting rings and an adhesive-bonding surface of each of the two metal armatures. The adhesive-bonding joint is made to extend from the end face of each supporting ring onto the lateral surface thereof and is filled in a vacuum-tight manner with a hardened layer of adhesive.
Fastened to one of the two metal armatures is an evaporator, which is kept at the potential of a high-voltage conductor, and fastened to the other armature is a condenser, which is kept at the potential of a grounded encapsulation. The high-voltage insulator forms an insulating clearance of a cooling element which transfers heat formed by current losses in the high-voltage conductor to the encapsulation. A working medium located inside the cooling element, such as acetone or a hydrofluoric ether, serves for the heat transfer and thereby circulates as a vapor from the evaporator through the insulating tube to the condenser, in which the vapor condenses as a liquid while giving off heat. The liquid is returned to the evaporator again through the high-voltage insulator. The high-voltage insulator therefore serves not only as an insulating clearance but also as a line for the working medium. Since this line receives a chemical medium, is exposed to a permanent temperature of 80° C., for example, and must be liquid-, gas- and vacuum-tight over many years, such as 20 years, the adhesive bonds between the two ends of the insulating tube that are respectively formed as a supporting ring and the metal armatures have to meet demanding requirements.